Animal of the Week July 9, 2012 -- Spot the difference #1

So, here is the first in a series (given my output perhaps of one) of ramblings about the differences between things. The idea was prompted by a text message from my sister Sarah on Sunday asking "What's the difference between shrimps & prawns". Fortunately I had recently investigated this myself, so was able to reply that it's actually more of a semantic thing than a phylogenetic thing; although on revisiting the subject, I find that actually that's not the whole story, and it really depends on who you speak to and where they are from.

Classic curvy prawn
(Penaeus monodon)

Classic shrimp back bend
(Pandalus borealis)

In certain fields, distinctions are made between shrimp and prawns. For example, taxonomists classify decapod crustaceans (a grouping that also includes crabs and lobsters) of the infraorder Caridea as shrimp and those of the suborder Dendrobranchiata as prawns. And to some extent this works for the scientists: shrimp have two pairs of pincers and a hooked body among other defining characters, and prawns have curved bodies and three pairs of pincers. However, many animals called shrimps (miracle shrimps, mantis shrimps, and some freshwater "shrimps") and some called prawns (the Dublin Bay prawn for example) belong to completely different groups of crustaceans—neither prawns nor shrimps.

In common day parlance, this division works in some circumstances. For once, the Aussies have it phylogenetically spot on. In Australia (sorry Sarah, I got this wrong), the phylogenetic distinction is quite rigorously enforced: prawns are those animals of the family Penaeidae (those most closely related to the tiger prawn), whereas shrimp are the Caridea.

Brown shrimp (Crangon crangon)

In England the size distinction between "prawns" and "shrimps" fits generally with the taxonomic division. The brown shrimp (Crangon crangon) caught around the UK, boiled, shelled, and "potted" deliciously in butter belongs to the Caridea and is indeed a shrimp, and big fat tiger prawns (Penaeus monodon) have a long curved body and three pairs of pincers, so are clearly prawns. However, the north Atlantic peeled prawn in the classic prawn cocktail (Pandalus borealis) is actually a shrimp. In North America the word prawn is rarely used, with even the largest members of the Dendrobranchiata being served as shrimp. To illustrate the problem further, the freshwater prawns of the genus Macrobrachium, popular in the cuisine of south and southeast Asia, are despite their large size, actually members of the Caridea. And in aquaculture, the term "shrimp farm" is becoming increasingly used for any attempts to cultivate any of these animals.
 

Prawn cocktail (phylogenetic shrimp)

So what is a prawn and what is a shrimp depends on your field of interest—phylogenetic, agricultural, or gustatory—and where you are from. The terms "prawn" and "shrimp" are both used as slang, again with regional preferences, to refer to someone who has a good body but an unattractive face, this use is derived from the practice of eating the body but throwing away the head of these crustaceans.